(20 min.) Case Study: Alignment and thermal growth

Michael Halstead, Vibration Technician, Searles Valley Minerals


At the facility where I work we have a chiller compressor that was a constant problem. It had vibration levels at 1.8 in/s and was constantly bieng shut down for repair. When we looked at the data we found there to be misalignment issues. Since the alignment reports that where turned in where acceptable we focused in on two things. Thermal growth and resonance issues. We performed a bump test and found there to be a resonant frequency close to running speed of the machine. We installed a tuned mass dampner then rechecked the machine. The misalignment was still present and the amplitude had been lowered but not enough. We then conducted a thorough investigation of the base and structure and found no defects. So with the dampner still installed we ran the machine and took thermal images of it. With these we calculated thermal growth. We also noticed that there was influence from the discharge piping. We then shutdown the machine and installed our laser alignment system and ran the thermal growth program from it. This gave us a better understanding of how the machine was affected in both the horizontal and the vertical directions. We applied what we learned to the next alignment and retested the machine. Now the machine was running at 0.21 in/s and has not been worked on in over a year and a half. I do have data that was collected and reports that where generated to for visual support in a presentation.

1. Better understanding of a complex alignment
2. Understand that compound issues can create problem for seemingly routine maintenance.
3. Provide examples of different methods to obtain good information that they can use to fix the problem.


I work at Searles Valley Minerals in Trona California. I have 17 years of experience as a maintenance journeyman and have been in the reliability group for 2 and a half years. Currently Cat II.